1 Battery junction box
2 Sheathed-type glow plug control module
3 Sheathed-type glow plug 1
4 Sheathed-type glow plug 2
5 Sheathed-type glow plug 3
6 Sheathed-type glow plug 4
7 PCM
8 Instrument cluster with glow plug warning indicator
The glow plug system of the Siemens common rail system is designed so that each sheathed-type glow plug is actuated separately.
For this purpose, the PCM transmits information on glow duration to the glow plug control module. The glow plug control module then actuates the
sheathed-type glow plugs.
In the case of a faulty sheathed-type glow plug (or when short circuit/open control loop occurs in a glow plug) this is detected by the glow plug control module and transmitted to the PCM.
In this way, a fault in the electrical circuit of a glow plug can be accurately pinpointed.
In order to calculate the glow time precisely, the PCM requires the following input signals:
โข ECT,
โข Engine speed (CKP signal),
โข BARO.
Generally, activation/deactivation of the sheathed-type glow plugs during the pre- and post-heating phases depends on the relevant ECT and BARO.
The relevant calibration data is stored as map data in the PCM and in addition to the ECT, BARO and engine speed, the injected fuel quantity (engine load condition) is also significant for the post heating process.
The on-time of the glow plug warning indicator is determined by the PCM. However, it does not provide any indication of the actual actuation times of the sheathed-type glow plugs. At low temperatures, the on-time of the glow plug warning indicator is shorter than the actuation time of the sheathed-type glow plugs.
The signal for the glow plug warning indicator is transmitted by PCM via the CAN bus to the gateway (instrument cluster or GEM) where the glow plug warning indicator is activated.
Preheating
The PCM receives the corresponding temperature signal from the ECT sensor.
The length of the preheating period depends on the temperature signal (low temperature = longer preheating period).
The driver is informed of preheating by the lit glow plug warning indicator in the instrument cluster. The preheating times become longer as the coolant temperature falls.
The BARO also has an influence on activation and deactivation of the sheathed-type glow plugs in the event of large altitude differences.
Example:
โข ECT = 60ยฐC, BARO = 0.95 bar:
โ Sheathed-type glow plug deactivated,
โข ECT = 60ยฐC, BARO